Allman / Neer Distal Third — Clavicle

Fractures of the distal third of the clavicle account for approximately 12–15% of all clavicle fractures and have distinct management considerations compared to mid-shaft fractures. The relationship of the fracture to the coracoclavicular (CC) ligaments — the conoid and trapezoid — determines the stability of the fracture and drives the decision to manage operatively or non-operatively. The Allman and Neer classifications are the most widely used frameworks.

• The distal clavicle is stabilised by the acromioclavicular (AC) ligaments (capsule and superior and inferior AC ligaments — control horizontal stability) and the coracoclavicular ligaments — conoid ligament (posteromedial, more vertical, primary restraint to superior displacement) and trapezoid ligament (anterolateral, more horizontal, primary restraint to axial compression)
• Mechanism: direct blow to the shoulder; fall on an outstretched hand; fall onto the point of the shoulder; direct impact in sports

• Key principle: the stability of a distal clavicle fracture depends entirely on the status of the CC ligaments relative to the fracture — if the CC ligaments remain attached to the medial fragment (Type I), the fracture is stable; if they are detached from the medial fragment (Type II, IIA, IIB, V), the medial fragment loses its inferior attachment to the coracoid and displaces superiorly due to trapezius pull — this is the unstable pattern with high non-union risk

• History and mechanism: direct shoulder blow, fall onto the shoulder; sporting injury; assess pain, shoulder function, skin integrity over the fracture
• Examination: tenderness and deformity at the distal clavicle; step deformity at the AC joint in Type II (clavicle displaced superiorly relative to the acromion); skin tenting in significantly displaced fractures (skin at risk); neurovascular assessment; assess contralateral shoulder for AC joint baseline
• Radiographs: standard AP clavicle and Zanca view (AC joint view — 15° cephalad tilt; better visualises the AC joint and distal clavicle); assess fracture pattern, displacement, and CC distance
• CC distance measurement on X-ray: measured from the superior cortex of the coracoid to the inferior cortex of the clavicle; normal approximately 11–13 mm; increased CC distance in Type II = superior displacement of the medial fragment; stress views (weight held in each hand) can demonstrate instability
• CT scan: for complex or comminuted fractures to better define anatomy and guide surgical planning; particularly for Type V comminuted fractures

• Neer Type I (stable): arm sling for comfort; early range of motion; progressive loading; union almost universal; return to sport at 6–8 weeks when comfortable
• Neer Type II (unstable) — surgical indications: Type II distal clavicle fractures have a reported non-union rate of 20–30% with non-operative management (some series up to 40%); surgical fixation is generally recommended; indications include: significant displacement, skin tenting, high-demand patients, bilateral fractures, open fracture; non-operative management can be considered in elderly low-demand patients or those with significant medical comorbidities
• Surgical options for Neer Type II:

• Hook plate removal: mandatory — the hook causes subacromial impingement and rotator cuff erosion if left in situ; removal planned at 3–6 months post-operatively once union is confirmed; failure to remove the hook plate is associated with subacromial pain, restricted ROM, and rotator cuff damage
• Neer Type III (intra-articular, stable): non-operative initially; late post-traumatic AC OA may develop in approximately 30%; distal clavicle excision (Mumford procedure) for symptomatic late OA

• Non-union of Neer Type II distal clavicle: symptomatic non-union (pain, weakness, instability) managed with open reduction, bone grafting, and fixation (hook plate or CC reconstruction); asymptomatic non-union may be managed non-operatively in low-demand patients; the distal fragment is usually small and requires careful handling; CC ligament reconstruction is often required alongside bony fixation
• K-wire migration: historically a well-documented and potentially fatal complication of percutaneous K-wire fixation across the AC joint; K-wires have migrated to the lung, heart, great vessels, and spinal canal; K-wire fixation for distal clavicle fractures has been largely abandoned; if used for other shoulder indications, bent K-wire ends should be left proud and patients followed closely with early removal
• Neer Type IV (paediatric periosteal sleeve fracture): in children, the clavicular periosteum is thick and strongly adherent; the medial fragment disrupts through the periosteum but the periosteal sleeve, CC ligaments, and distal clavicle remain intact; the fracture appears like an AC dislocation radiologically but is actually a fracture-separation; the periosteal sleeve allows reliable remodelling — non-operative management and excellent outcomes in children; surgical intervention rarely required
• Distinguishing AC joint dislocation from Neer Type II distal clavicle fracture: both present with superior displacement of the lateral clavicle relative to the acromion; the key radiological distinction is the CC ligament status — in AC dislocation, the clavicle is intact and the CC ligaments are disrupted; in Neer Type II, the clavicle is fractured and the CC ligaments are detached from the medial fragment; careful review of the AP X-ray (looking for the fracture line) and a Zanca view are essential

• Stability determined by CC ligament attachment to medial fragment: CC intact to medial fragment = stable (Type I); CC detached from medial fragment = unstable (Type II) = high non-union risk
• Neer Type I: lateral to CC; CC intact to medial fragment; stable; non-operative; >95% union
• Neer Type II: medial to or through CC ligaments; CC detached from medial fragment; unstable; 20–40% non-union non-operatively; surgical fixation recommended
• Type IIA: both CC intact to distal fragment; Type IIB: conoid torn; trapezoid attached to distal fragment
• Neer Type III: intra-articular; stable; non-operative; late ACJ OA → Mumford procedure
• Hook plate: most widely used technique for Type II; MUST be removed at 3–6 months — subacromial impingement + rotator cuff erosion if left in situ
• K-wire fixation: ABANDONED — migration risk (thorax, heart, vessels); serious and potentially fatal complication
• Neer Type IV: paediatric periosteal sleeve fracture; mimics AC dislocation; non-operative with excellent remodelling
• CC distance: normal 11–13 mm; increased = Type II displacement; Zanca view best for imaging the distal clavicle
• Coracoclavicular ligaments: conoid (posteromedial, vertical) primary restraint to superior displacement; trapezoid (anterolateral, horizontal) primary restraint to axial load